The present invention relates to metals, in particular tantalum, and products made from tantalum as well as methods of making and processing the tantalum.
In industry, there has always been a desire to form higher purity metals for a variety of reasons. With respect to tantalum, higher purity metals are especially desirable due to tantalum's use as a sputtering target and its use in electrical components such as capacitors. Thus, impurities in the metal can have an undesirable effect on the properties of the articles formed from the tantalum.
When tantalum is processed, the tantalum is obtained from ore and subsequently crushed and the tantalum separated from the crushed ore through the use of an acid solution and density separation of the acid solution containing the tantalum from the acid solution containing niobium and other impurities. The acid solution containing the tantalum is then crystallized into a salt and this tantalum containing salt is then reacted with pure sodium in a vessel having an agitator typically constructed of nickel alloy material, wherein tungsten or molybdenum is part of the nickel alloy. The vessel will typically be a double walled vessel with pure nickel in the interior surface. The salt is then dissolved in water to obtain tantalum powder. However, during such processing, the tantalum powder is contaminated by the various surfaces that it comes in contact with such as the tungsten and/or molybdenum containing surfaces. Many contaminants can be volatized during subsequent melting, except highly soluble refractory metals (e.g., Nb, Mo, and W). These impurities can be quite difficult or impossible to remove, thus preventing a very high purity tantalum product.
Accordingly, there is a desire to obtain higher purity tantalum products which substantially avoid the contaminations obtained during the processing discussed above. Also, there is a desire to have a tantalum product having higher purity, a fine grain size, and/or a uniform texture. Qualities such as fine grain size can be an important property for sputtering targets made from tantalum since fine grain size can lead to improved uniformity of thickness of the sputtered deposited film. Further, other products containing the tantalum having fine grain size can lead to improved homogeneity of deformation and enhancement of deep drawability and stretchability which are beneficial in making capacitors cans, laboratory crucibles, and increasing the lethality of explosively formed penetrators (EFP's). Uniform texture in tantalum containing products can increase sputtering efficiency (e.g., greater sputter rate) and can increase normal anisotropy (e.g., increased deep drawability), in preform products.